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Abstract:

AFM tweezers includes: a first probe that comprises a triangular prism
member having a ridge, a tip of which is usable as a probe tip in a
scanning probe microscope; a second probe that comprises a triangular
prism member provided so as to open/close with respect to the first
probe. The first probe and the second probe are juxtaposed such that a
predetermined peripheral surface of the triangular prism member of the
first probe and a predetermined peripheral surface of the triangular
prism member of the second probe face substantially in parallel to each
other, and the first probe formed of a notch that prevents interference
with a sample when the sample is scanned by the tip of the ridge.

Claims:

1. AFM tweezers comprising:a first probe that comprises a triangular prism
member having a ridge, a tip of which is usable as a probe tip in a
scanning probe microscope;a second probe that comprises a triangular
prism member provided so as to open/close with respect to the first
probe, wherein:the first probe and the second probe are juxtaposed such
that a predetermined peripheral surface of the triangular prism member of
the first probe and a predetermined peripheral surface of the triangular
prism member of the second probe face substantially in parallel to each
other, andthe first probe formed of a notch that prevents interference
with a sample when the sample is scanned by the tip of the ridge.

2. AFM tweezers according to claim 1, whereinthe notch is configured such
that a predetermined region of the ridge in a vicinity of the tip of the
ridge is void to provide a wedge shape portion including the tip of the
ridge, the wedge being arranged in a direction of the ridge.

3. A scanning probe microscope comprising:the AFM tweezers according to
claim 1;a scanning driving unit that relatively moves the AFM tweezers
with respect to a sample to perform scanning driving of the tip of the
ridge of the first probe to scan the sample;an opening/closing driving
unit that opens/closes the second probe; anda detecting unit that detects
a displacement of the first probe upon the scanning driving, wherein:a
surface configuration of the sample is determined based on the
displacement detected by the detecting unit.

4. A scanning probe microscope according to claim 3, wherein:assuming that
a height of the sample from a mounting surface on which the sample is
placed is d1 and an angle between the mounting surface and the ridge is
θ deg, a notch surface of the notch comprisesa first notch surface
that passes between the tip of the ridge and a position on the ridge at a
distance of d1/(2 sin θ) from the tip and that is at an angle of
(90-.theta.) to the ridge; anda second notch surface that passes a
position on the ridge at a distance of d1/sin θ from the tip of the
ridge and that is orthogonal to the first notch surface.

5. A scanning probe microscope according to claim 4, wherein:the first
notch surface is provided with a nanotube perpendicular to the mounting
surface, with a tip of the nanotube protruding closer to the mounting
surface than an end of the first probe on the side of the mounting
surface, so that the tip of the nanotube is used as a probe tip for
observation.

6. A scanning probe microscope according to claim 5, further comprising:a
drive control unit that controls the AFM tweezers to be moved such that a
lower end of the first probe is moved to a predetermined height from the
mounting surface and the first and the second probes to close to grip the
sample, wherein:an amount of protrusion of the nanotube is set to be
greater than the predetermined height.

7. A scanning probe microscope according to claim 4, wherein:the first
notch surface that passes the tip on the ridge is configured such that a
size of a portion including the tip of the ridge in a direction
perpendicular to the first notch surface is decreased, anda protrusion
protruding toward the mounting surface is provided on the second notch
surface of the first probe such that a distance between the protrusion
and the mounting surface is greater than a distance between the tip and
the mounting surface, and the distance between the protrusion and the tip
is smaller than a size of the sample in a direction along the mounting
surface.

8. A method for producing the AFM tweezers according to claim 1,
comprising:processing a semiconductor wafer by a photolithographic
process to fabricate the first and the second probes.

9. A method for producing the AFM tweezers according to claim 8,
wherein:the first probe is processed by the photolithographic process to
form the notch.

10. A method for producing the AFM tweezers according to claim 8,
wherein:a region in which the notch of the first probe is to be formed is
exposed to a focused ion beam to form the notch.

11. A method for producing the AFM tweezers according to claim 8,
wherein:tips of the first and the second probes are exposed to a focused
ion beam in a state in which the first and the second probes are closed
to make lengths and heights of the tips of the first and second probes
uniform therebetween.

Description:

INCORPORATION BY REFERENCE

[0001]The disclosure of the following priority application is herein
incorporated by reference:

[0004]The present invention relates to AFM (Atomic Force Microscope)
tweezers with a probe that can be used as a probe tip for use in a
scanning probe microscope, to a method for producing such AFM tweezers,
and to a scanning probe microscope.

[0005]2. Description of Related Art

[0006]So-called AFM tweezers that include two probes between which a
sample is to be inserted and grip/release the sample have been developed
to be applied to manipulation of samples to be observed by a scanning
probe microscope.

[0007]Such AFM tweezers in a cantilever used in, for example, a scanning
probe microscope include the following: (1) AFM tweezers including two
carbon nanotubes attached to a probe tip attached to the tip of a
cantilever made of silicon (see Japanese Laid-Open Patent Publication No.
2001-252900); (2) AFM tweezers including carbon nanotubes attached to a
glass tube that serves as a cantilever; and (3) AFM tweezers including
two cantilevers fabricated on a silicon substrate by a MEMS (Micro
Electro Mechanical Systems) process.

[0008]In the tweezers (1) and (2) above, electrostatic electricity is
applied between carbon nanotube probe tips to open/close the two carbon
nanotubes. Examples of the tweezers (3) above include the following. In
one example, current is applied to bases of the cantilevers of the
tweezers to generate heat and linear expansion of silicon cantilevers due
to the generated heat is amplified to drive the cantilevers. In another
example, a comb-shaped electrostatic actuator is provided to enable the
two cantilevers to grip an object therebetween (see Tetsuya Takekawa, Gen
Hashiguchi, Eiichi Tamiya, et al., "Study of AFM tweezers for
manipulation of nano objects", Extended Summary of The Institute of
Electrical Engineers of Japan, Trans. AFM, Vol. 125, No. 11, 2005).

[0009]Conventional devices, however, are each configured to grip a sample
with very thin carbon nanotubes, so that they grip the samples only
unstably and manipulations for gripping are difficult to do. The AMP
tweezers described in "Study of AFM tweezers for manipulation of nano
objects" include a knife-edged probe, and the shape of the probe tip is
reflected on the obtained AFM image to produce a false image. As a
result, shape information such as width and height of the sample gripped
by the tweezers is difficult to obtain.

SUMMARY OF THE INVENTION

[0010]AFM tweezers according to a first aspect of the present invention
includes: a first probe that comprises a triangular prism member having a
ridge, a tip of which is usable as a probe tip in a scanning probe
microscope; a second probe that comprises a triangular prism member
provided so as to open/close with respect to the first probe, wherein:
the first probe and the second probe are juxtaposed such that a
predetermined peripheral surface of the triangular prism member of the
first probe and a predetermined peripheral surface of the triangular
prism member of the second probe face substantially in parallel to each
other, and the first probe formed of a notch that prevents interference
with a sample when the sample is scanned by the tip of the ridge.

[0011]According to a second aspect of the present invention, in the AFM
tweezers according to the first aspect, the notch may be configured such
that a predetermined region of the ridge in a vicinity of the tip of the
ridge is void to provide a wedge shape portion including the tip of the
ridge, the wedge being arranged in a direction of the ridge.

[0012]A scanning probe microscope according to a third aspect of the
present invention includes: the AFM tweezers according to the first
aspect; a scanning driving unit that relatively moves the AFM tweezers
with respect to a sample to perform scanning driving of the tip of the
ridge of the first probe to scan the sample; an opening/closing driving
unit that opens/closes the second probe; and a detecting unit that
detects a displacement of the first probe upon the scanning driving,
wherein: a surface configuration of the sample is determined based on the
displacement detected by the detecting unit.

[0013]According to a fourth aspect of the present invention, in the
scanning probe microscope according to the third aspect, assuming that a
height of the sample from a mounting surface on which the sample is
placed is d1 and an angle between the mounting surface and the ridge is
θ deg, it is preferable that a notch surface of the notch includes:
a first notch surface that passes between the tip of the ridge and a
position on the ridge at a distance of d1/(2 sin θ) from the tip
and that is at an angle of (90-θ) to the ridge; and a second notch
surface that passes a position on the ridge at a distance of d1/sin
θ from the tip of the ridge and that is orthogonal to the first
notch surface.

[0014]According to a fifth aspect of the present invention, in the
scanning probe microscope according to the fourth aspect, the first notch
surface may be provided with a nanotube perpendicular to the mounting
surface, with a tip of the nanotube protruding closer to the mounting
surface than an end of the first probe on the side of the mounting
surface, so that the tip of the nanotube is used as a probe tip for
observation.

[0015]According to a sixth aspect of the present invention, in the
scanning probe microscope according to the fifth aspect, a drive control
unit may be further included that controls the AFM tweezers to be moved
such that a lower end of the first probe is moved to a predetermined
height from the mounting surface and the first and the second probes to
close to grip the sample, and it is preferable that an amount of
protrusion of the nanotube is set to be greater than the predetermined
height.

[0016]According to a seventh aspect of the present invention, in the
scanning probe microscope according to the fourth aspect, the first notch
surface that passes the tip on the ridge may be configured such that a
size of a portion including the tip of the ridge in a direction
perpendicular to the first notch surface is decreased, and a protrusion
protruding toward the mounting surface may be provided on the second
notch surface of the first probe such that a distance between the
protrusion and the mounting surface is greater than a distance between
the tip and the mounting surface, and the distance between the protrusion
and the tip is smaller than a size of the sample in a direction along the
mounting surface.

[0017]According to a eighth aspect of the present invention, in a method
for producing the AFM tweezers according to the first aspect, a
semiconductor wafer is processed by a photolithographic process to
fabricate the first and the second probes.

[0018]According to a ninth aspect of the present invention, in the method
for producing the AFM tweezers according to the eighth aspect, the first
probe may be processed by the photolithographic process to form the
notch.

[0019]According to a tenth aspect of the present invention, in the method
for producing the AFM tweezers according to the eighth aspect, it is
preferable that a region in which the notch of the first probe is to be
formed is exposed to a focused ion beam to form the notch.

[0020]According to a eleventh aspect of the present invention, in the
method for producing the AFM tweezers according to the eighth aspect,
tips of the first and the second probes may be exposed to a focused ion
beam in a state in which the first and the second probes are closed to
make lengths and heights of the tips of the first and second probes
uniform therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 schematically illustrates an atomic force microscope equipped
with AFM tweezers according to an embodiment of the present invention;

[0023]FIG. 3 illustrates the shape of an observation probe in a front
view, a top view, and a side view;

[0024]FIG. 4A illustrates the function of AFM tweezers in an observation
state and FIG. 4B illustrates the function of AFM tweezers in a gripping
state;

[0025]FIG. 5A illustrates a wedge-shaped observation probe while
performing an action of observation, with L1 indicating a trajectory of
the tip of the observation probe upon AFM observation and FIG. 5B shows
an observed image obtained with the observation probe shown in FIG. 5A;

[0026]FIG. 6A illustrates a wedge-shaped observation probe with a notch
while performing an action of observation, with L2 indicating a
trajectory of the tip of the observation probe upon AFM observation and
FIG. 6B shows an observed image obtained with the observation probe shown
in FIG. 6A;

[0028]FIG. 8A shows an observation probe according to a first modification
of the present invention, FIG. 8B shows an observation probe according to
a second modification of the present invention, and FIG. 8C shows an
observation probe according to a third modification of the present
invention;

[0029]FIG. 9A shows a gripping probe according to a first example of the
present invention, FIG. 9B shows a gripping probe according to a second
example of the present invention and FIG. 9c shows a gripping probe
according to a third example of the present invention;

[0030]FIG. 10 illustrates processes a to c in a method for producing AFM
tweezers according to an embodiment of the present invention, with (a1)
and (a2) illustrating a step a, (b1) and (b2) illustrating a step b, and
(c1) and (c2) illustrating a step c;

[0031]FIG. 11 shows a mask M1;

[0032]FIG. 12 illustrates processes d and e in a method for producing AFM
tweezers according to an embodiment of the present invention, with (a1)
and (a2) illustrating a step d, and (b1) to (b3) illustrating a step e;

[0034]FIG. 14 illustrates steps f and g in a method for producing the AFM
tweezers according to an embodiment of the present invention, with (a1)
and (a2) illustrating a step f, and (b1) and (b2) illustrating a step g;

[0037]FIG. 17 illustrates a process of processing the tip of an
observation probe with a convergent ion beam;

[0038]FIG. 18A shows an observation probe with a carbon nanotube attached
to a tip thereof according to a second embodiment of the present
invention and FIG. 18B illustrates elastic buckling of the carbon
nanotube upon gripping by therewith;

[0039]FIG. 19 shows a second probe tip formed in the observation probe;

[0040]FIG. 20 illustrates adjustment of the length and height of the
probe;

[0041]FIG. 21 is a graph plotting sample size vs. grippable range
illustrating an example of grippable range when the observation probe is
not formed of a notched portion;

[0042]FIGS. 22A to 22C illustrate fabrication of a notched portion by
anisotropic etching; and

[0043]FIG. 23 illustrates fabrication of a notched portion by ICR-RIE.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0044]The following explains a best mode for carrying out the invention
with reference to the attached drawings. FIG. 1 schematically illustrates
an atomic force microscope (hereafter, referred to as "AFM device"),
which is a kind of a scanning probe microscope (SPM).

[0045]The AFM device includes AFM tweezers 1, a laser beam source 2, a
2-part or 4-part divided photodiode 3, a control unit 4, an excitation
unit 5, an electrostatic actuator 6, a three-dimensional stage 8, and a
driver circuit unit 9. The AFM tweezers 1, which include a stationary arm
10 and a movable arm 20 on a support 25, are fabricated by processing an
SOI (Silicon on Insulator) wafer by using a photolithographic technology
as described later on.

[0046]The stationary arm 10 includes a lever 10A and an observation probe
10B provided on a tip of the lever 10A. When AFM observation is performed
with the AFM tweezers 1, a surface of an observation object is scanned
with the observation probe 10B. The movable arm 20 includes a lever 20A
and a gripping probe 20B provided on a tip of the lever 20A. The
observation probe 10B and the gripping probe 20B are arranged
substantially parallel to each other at a predetermined distance from
each other. The movable arm 20 is driven to open/close the tweezers by
the electrostatic actuator 6, which is comb-shaped.

[0047]The support 25 is removably held by a holder (not shown). The holder
by which the support 25 is held is fixed on the three-dimensional stage 8
provided in the AFM device. By driving the three-dimensional stage 8, the
AFM tweezers 1 in whole can be moved in each of x, y, and z directions
accordingly. The support 25 can be attached to the holder in various
manners. For example, the support 25 may be slid into a groove or concave
portion formed in the holder to be fitted therein, or the support 25 may
be sandwiched by leaf springs attached to the holder.

[0048]The laser beam source 2 emits a laser beam, which is irradiated onto
an upper surface of the stationary arm 10 to generate reflected laser
beam. The reflected laser beam is detected by the 2-part or 4-part
divided photodiode 3 to create a detection signal. The detection signal
from the 2-part or 4-part divided photodiode 3 is input to the control
unit 4, which control the AFM device in whole. The control unit 4
calculates a change in displacement or vibration state (amplitude,
frequency, and phase) of the stationary arm 10 based on the detection
signal and controls the units such that an amount of change in
displacement or vibration state will be constant and a surface profile of
the sample is measured. The results of the measurement are displayed on,
for example, a monitor (not shown). Though not shown, the excitation unit
5 is provided with a piezoelectric element that vibrates the AFM tweezers
1 in whole in the z direction to vibrate the stationary arm 10 and a
driving unit that drives the piezoelectric element.

[0049]FIG. 2 is a schematic perspective view showing the AFM tweezers 1 as
seen from the rear side (from the -z direction). The electrostatic
actuator 6 includes a comb-shaped stationary electrode 60 fixed to the
support 25 and a comb-shaped movable electrode 61 connected to the
movable arm 20. Arm opening/closing voltage is applied between the
stationary electrode 60 and the movable electrode 61 by the driving
circuit unit 9 to open/close the arm.

[0050]The movable electrode 61 is supported on the support 25 by an
elastic support section 62. The elastic support section 62 is linked to
the movable arm 20 through a linking member 63. With this construction,
when arm opening/closing voltage is controlled so as to drive the movable
electrode 61 in the x direction, the movable arm 20 is driven in a
direction in which the AFM tweezers 1 are closed. As a result, a sample,
which is present between the observation probe 10B and the gripping probe
20B, can be gripped therebetween.

[0051]The gripping probe 20B is a wedge-shaped probe having a rectangular
triangle cross-section with its ridge being facing the -z direction. On
the other hand, the observation probe 10B is generally a wedge-shaped
probe having a rectangular triangle cross-section similarly to the
gripping probe 20B. In the gripping probe 20B, however, a part of the
ridge taking the form of an acute angle and facing toward the -z
direction (direction of observation sample) is notched to form a probe
tip section 110 at the tip thereof. The observation probe 10B and the
gripping probe 20B are arranged in juxtaposition such that vertical
surfaces of the wedge-shaped probes face each other substantially in
parallel.

[0052]FIG. 3 illustrates the shape of an observation probe 10B in a front
view, a top view, and a side view. As shown in the part of the side view
(down left), a notch 100 is formed along a part of the ridge to form a
probe tip section 110 for AFM observation on the tip of the observation
probe 10B. The observation probe 10B approaches to an observation plane
at a tilt and the tip (designated by P) of the ridge of the probe tip
section 110 is used as a probe tip. A vertical surface 112 of the
observation probe 10B facing the gripping probe 20B is used as a gripping
surface. A two-dot chain line indicates an edge region deleted when the
notch 100 is formed.

<<AFM Observation>>

[0054]The AFM tweezers 1 according to the present embodiment serve as
tweezers that grip a sample between the observation probe 10B and the
gripping probe 20B and convey it and as a probe tip that performs AFM
observation of the sample. As shown in FIG. 4A, when AFM observation is
performed by using the AFM tweezers 1, the observation object is scanned
by the probe tip section 110 formed on the tip of the observation probe
10B.

[0055]When observation is performed in a contact mode, the probe tip
section 110 is moved in contact with the observation surface to perform
XY scanning. On the other hand, when observation is performed in a
dynamic force mode, XY scanning is performed while the observation probe
10B approached close to the observation surface is being resonantly
vibrated up and down as shown in FIG. 4A.

[0056]When a distance (an average distance in the case of the dynamic
force mode) between the tip of the probe tip section 110 and the
observation object is changed due to unevenness of the surface of the
observation object, an interaction between the surface of the observation
object and the probe tip section 110 is changed. As a result, the lever
10A to which laser beam is irradiated is bent in the direction of up and
down in the contact mode while the state of vibration of the lever 10A is
changed in the dynamic force mode. These changes are measured by an
optical lever measuring method in which the laser beam source 2 and the
2-part or 4-part photodiode 3 are used.

[0057]When the observation is performed in a dynamic force mode, the
piezoelectric element provided in the excitation unit 5 is driven so as
to vibrate the AFM tweezers 1 in whole in the z direction in order to
resonantly vibrate at a large amplitude only the stationary arm 10 in the
z direction as shown in FIG. 4A. On this occasion, vibration of only the
stationary arm 10 can be achieved by design. That is, by designing the
levers 10A and 20A such that a resonant vibration frequency f1 of the
stationary arm 10 is higher than a resonant vibration frequency f2 of the
movable arm 20 and setting the vibration frequency of the excitation unit
5 to the resonant vibration frequency ft, only the stationary arm 10 can
be vibrated at a large amplitude.

<<Gripping of Sample>>

[0059]FIG. 4B illustrates gripping of a sample with the tweezers 1. When
gripping the sample, direct current probe opening/closing voltage is
applied and the level of voltage is controlled as mentioned above to
perform closing driving of the movable arm 20, i.e., to move the movable
arm 20 toward the stationary arm 10. As a result, the sample is gripped
between the gripping probe 20B and the observation probe 10B. As
mentioned above, the surfaces of the observation probe 10B and the
gripping probe 20B facing each other are both vertical, so that the
sample is gripped between the vertical surfaces.

<<Explanation on Shape of Observation Probe 10B>>

[0061]In the present embodiment, in order to enable gripping of the sample
to be performed stably, the tweezers 1 are configured as follows. That
is, the wedge-shaped observation probe 10B and the wedge-shaped gripping
probe 20B are arranged such the vertical surfaces of thereof are opposite
to each other, so that the sample can be gripped therebetween. When AFM
observation is performed, the tip of the lower ridge of the observation
probe 10B is used as a probe tip.

[0062]However, if the observation probe 10B has a shape similar to that of
the gripping probe 20B, there will occur an inconvenience as shown in
FIGS. 5A and 5B. The observation probe 10A shown in FIGS. 5A and 5B has a
wedge shape similar to that of the gripping probe 20B. FIG. 5A
illustrates the trajectory of the tip of an observation probe 11B upon
AFM observation and FIG. 5B shows the observed image.

[0063]FIGS. 5A and 53 illustrate an example in which a spherical sample
300 mounted on an observation stage 302 is observed. As shown in FIG. 5A,
the observation probe 11B is held at a tilt to a mounting surface of the
observation stage 302 and approached down near the surface of the
observation surface 302. Thereafter, the observation probe 11B is driven
to scan in the direction of right and left in the figures. A broken line
L1 indicates a trajectory of the tip of the observation probe 11B. Upon
the AFM observation, the surface configuration of the observation object
is measured based on the trajectory L1 of the observation probe 11B and
the shape of a curve including a set of the trajectories L1 corresponds
to the surface configuration of the observation object.

[0064]FIG. 5B is a plan view of the observation image 304 of the sample
300 obtained by the scanning shown in FIG. 5A. Since the sample 300 is
spherical, it is desirable that the obtained image is circular. However,
the observed image 304 shown in FIG. 5B is not in left-right symmetry and
the right hand side (portion designated by 304a) of the observed image
304 is trailing. This is because when the tip of the observation probe
11B reaches a point P1 in FIG. 5A, the lower ridge of the observation
probe 11B comes to interfere with the sample 300. As a result, the
observation probe 11B is caused to scan such that the tip of the
observation probe 11B is moved in a straight line on the trajectory L1
obliquely in the direction toward upper left to provide the observed
image 304 as shown in FIG. 55.

[0065]The AFM tweezers 1 according to the present embodiment is configured
such that a part of the lower ridge of the observation probe 10B is
formed of the notch 100 as shown in FIG. 3. This is to decrease the
interference between the ridge portion and the sample upon scanning.
FIGS. 6A and 6B illustrate the observed image obtained with the
observation probe 10B.

[0066]FIG. 6A illustrates the trajectory L2 of the tip of the observation
probe. Since the observation probe 10B is formed of the notch 100, the
surface configuration of the observation stage 302 is observed until the
probe tip section 110 approaches to a position in the vicinity of the
sample 300 (position indicated by a point P2). As a result, the trailing
portion 304a is decreased to a minimal level in the observed image 304
shown in FIG. 6B, so that the observed 304 that has a close resemblance
to the actual configuration of the sample 300 can be obtained.

[0067]FIG. 7 illustrates the shape of the observation probe. As mentioned
above, the AFM tweezers 1 are held such that an angle between the
observation probe 10B and the observation stage 302 is a predetermined
angle θ so that AFM observation can be performed with the tip of
the ridge of the observation probe 10B. A notch surface of the notch 100
includes a notch surface 100a that is vertical to the mounting surface of
the observation stage 302 and a notch surface 100b that is parallel to
the mounting surface of the observation stage 302.

[0068]It is assumed that a distance of the notch surface 100b from the
lower end of the probe tip section 110 is d1. If a diameter of the
spherical sample 300 mounted on the observation stage 302 is smaller than
the distance d1, the sample 300 comes in under the notch surface 100b
when the observation probe 10B scans in the direction toward left as
indicated by arrow in FIG. 6A. This allows the probe tip section 110 to
approach to the sample 300 to a position at which the vertical notch
surface 100a almost contacts the sample 300.

[0069]As a result, as shown in FIGS. 6A and 6B, the configuration of the
sample 300 can be measured more exactly than conventionally, so that the
performance of the AFM observation can be improved. For example, assuming
that a size of the notch surface 100b in the direction of right and left
in FIG. 7 is d2, the length of the tail portion of the observed image 304
can be decreased by around [d2-d1/2-(d1/tan θ-D/tan θ)] than
the case where the observation probe 11B is used. Here, D is a diameter
of the spherical sample 300 and it is assumed that D≦d1. Assuming
that a height of the sample from the mounting surface is d1 and an angle
between the mounting surface and the ridge of the observation probe is
θ, the notch surface 100a passes between the tip of the ridge and a
position on the ridge at a distance of d1/(2 sin θ) from the tip at
an angle of (90-θ) to the ridge. Moreover, The notch surface 100b,
which is orthogonal to the notch surface 100a, passes a position of the
ridge at a distance of d1/sin θ from the tip of the ridge. Assuming
that a size d4 of the ridge at the probe tip section 110 is 0, i.e.,
d4=0, the tail portion of the observed image 304 is formed only to a
negligible extent, if any.

[0070]Of course, when the diameter of the sample 300 becomes greater than
d1, the ridge of the observation probe 10B interferes with the sample 300
before the notch surface 100a comes close to the sample 300. As a result,
the tail portion 304a of the observed image 304 becomes greater than the
case where the diameter of the sample 300 is smaller than d1.

[0071]The gripping performance of the AFM tweezers provided with the notch
100 is as follows. To simplify explanation, explanation is made on an
example in which the spherical sample 300 is to be gripped. When the
spherical sample 300 has a diameter of d1, the sample 300 can be gripped
between the observation probe 10B and the gripping probe 20B if a
position of the center of the sample 300 is in a region d3 when the
gripping probe 20B is closed. The straight line L10 passes the center of
the spherical sample 300 and is parallel to the surface of the
observation stage 302. Assuming that the length of the ridge of the
gripping section 110 is d4, the size d3 in the horizontal direction of
the gripping section 110 can be expressed by formula (1) below:

d3=d4 cos θ+(d1/2)tan θ (1)

[0072]On the other hand, when the notch 100 is not formed in the
observation probe 10B, the horizontal size d5 with which the spherical
sample 300 can be gripped can be expressed by formula (2) below. The
two-dot chain line indicates the ridge in the case where the notch is not
formed. That is, by forming the notch 100, the grippable range in which
the sample 300 can be gripped is decreased by Δd shown in formula
(3) below.

d5=(d1/2)(tan θ+1/tan θ) (2)

Δd=(d1/2)/tan θ-d4 cos θ (3).

[0073]As can be seen from FIG. 7, as the diameter of the sample 300
becomes smaller and smaller than d1, the ratio d3/d5 gradually approaches
to 1 and when the diameter of the sample 300 is smaller than 2d4 sin
θ, there is obtained; d3/d5=1. That is, the influence of the
provision of the notch 100 on the gripping performance is null. In
addition, d4 may be set as indicated by formula (4) in order to make
Δd=0. In this case, the tail portion in the observed image can be
decreased while maintaining the gripping performance as high as the case
where the notch 100 is not provided.

d4=d1/(2 sin θ) (4)

[0074]When the height d1 of the notch surface 100b is increased in order
to make it possible to perform observation of a greater sample with good
precision, a cross-sectional area of a neck portion 120 where the notch
surface 100b and the notch surface 100a cross each other becomes too
small to maintain the strength of the observation probe 10B. Therefore,
when the height d1 of the notch surface is increased, the neck portion
120 is formed to have a slant notch surface 100c as shown in FIG. 8A, so
that the neck portion 120 does not become too thin.

[0075]That is, the configuration of the notch 100 is determined depending
on the length of the ridge region (shown in two-dot chain line). The
notch surface 100c is a plane parallel to the upper surface of the
observation probe 10b and connects the notch surface 100a and the notch
surface 100b to each other. In FIG. 8A, the solid line indicates the case
where the height of the notch surface 100b is d11, the broken line
indicates the case where the height of the notch surface 100b is d1, and
the dashed dotted line indicates the case where the height of the notch
surface 100b is d12 (>d11).

[0076]FIG. 8B shows an observation probe according to another modification
of the present invention. In the observation probe 10B shown in FIG. 8B,
a slant notch surface 100d is formed instead of the vertical notch
surface 100a shown in FIG. 7. The notch surface 100d is at an angle of
θ2 with respect to a vertical plane. In this case, the tail portion
304a of the observed image 304 becomes somewhat greater than the vertical
notch surface 100a. The gripping performance, however, can be improved
because the size d3 is increased. The size d3 is given by formula (5)
below and is greater than the size d3 of the observation probe 10B shown
in FIG. 7 by the second term in the right-hand side of the formula (5).

d3={d4 cos θ+(d1/2)tan θ}+(d1/2-d4 sin θ)tan θ2}
(5)

[0077]FIG. 8C shows a third modification of the observation probe 10B. In
the third modification, a slant notch surface 100e is formed instead of
the notch surface 100b parallel to the scanning surface of the
observation probe 10B shown in FIG. 8B. With this configuration, the tail
portion 304a can be decreased when a greater sample is scanned.

[0078]FIGS. 9A to 9C show the gripping probes with differently shaped
vertical planes that serve as gripping surfaces. FIG. 9A shows the
gripping probe 20B shown in FIG. 2. The two-dot chain line indicates the
shape of the gripping surface of the observation probe 10B. When the
sample 300 as shown in FIG. 9A is gripped, stability of gripping is
improved since in spite of the relatively small contact surface of the
gripping surface of the observation probe 103, the contact surface of the
gripping probe 205 is relatively large.

[0079]In FIG. 9B, the gripping probe 20B has a shape similar to that of
the observation probe 10B, and a portion that faces the probe tip section
110 of the observation probe 10B is made a gripping section 200. In FIG.
9C, the size of the gripping section 200 facing the probe tip section 110
of the observation probe 103 is made larger than the case shown in FIG.
9B to make it easy to grip the sample 300.

<<Size of Sample and Grippable Range>>

[0081]Explanation is made on grippable range taking an example in which a
spherical sample is to be manipulated. First, in the case where the notch
100 is not formed, assuming the angle θ between the observation
probe 10B and the surface of the sample is 13 degrees, the grippable
range is as shown in FIG. 21. The grippable range for typical diameters
of samples is as shown in the following table. For example, when the
diameter of the sample is 100 nm, the grippable range in which such
sample can be gripped is 200 nm.

[0082]On the other hand, when the notch 100 is formed, if the diameter of
the sample is greater than 2d4 sin θ, the grippable range is
smaller than ever by the formula (3) above. Accordingly, the shapes of
the tips of the observation probe 10B and the gripping probe 20B should
be determined in a comprehensive manner based on the grippable range,
processing precision of notch, precision of matching the probes,
positioning precision of the three-dimensional stage, the strength of the
observation probe 10B, and so on.

<<Production Method for AFM Tweezers 1>>

[0084]Explanation is made on a production method for AFM tweezers 1. The
AFM tweezers 1 according to the present embodiment is integrally formed
from an SOI (Silicon on Insulator) wafer. As will be detailed later on,
the support 25 includes a Si layer, a SiO2 layer, and a lower Si
layer that constitute the SOI wafer. The stationary arm 10, the movable
arm 20, and the electrostatic actuator are formed on the upper Si layer.
In the present embodiment, a SOI wafer having the thicknesses of the
upper Si layer, the SiO2 layer, and the lower Si layer of 6 μm, 1
μm, and 300 μm, respectively, is used. However, the combination of
the sizes is not limited to the above-mentioned example.

[0085]FIGS. 10 to 16 illustrate a process for producing the AFM tweezers 1
according to the present embodiment. The process includes steps a to g
that are carried out in order. In FIG. 10, (a1) and (a2) illustrate the
step a. (a1) is a perspective view and (a2) is a cross-sectional view. In
the step a, a SOI wafer 30 including an upper Si layer 31, a SiO2
layer 32, and a lower Si layer 33 is provided, and a silicon nitride
(SiN) film 34 having a thickness of 50 nm is formed on the upper Si layer
31. The upper Si layer 31 of the SOI wafer 30 is configured such that its
surface is a main surface Si(001) of a Si single crystal.

[0086]In FIG. 10, (b1) and (b2) illustrate the step b. (b1) is a
perspective view and (b2) is an R-R cross-sectional view.

[0087]In the step b, the SiN film 34 is partially etched off by RIE
(Reactive Ion Etching with C2F6 using a mask M1 shown in FIG.
11 to expose a portion of the upper Si layer 31 (outline region A1). The
region A1 in which the SiN film 34 has been etched off is a region in
which the stationary arm 10, the movable arm 20, and the electrostatic
actuator 6 are formed. The <110> direction of the upper Si layer 31
is selected as the direction in which the tips of the stationary arm 10
and the movable arm 20 extend.

[0088]The mask M1 shown in FIG. 11 includes the region of the support 25.
The portion shown in (b1) in FIG. 10 relates to the region above an R1-R1
line in FIG. 11. In the following, the region upper than the R1-R1 line
is described.

[0089]In FIG. 10, in the step c shown in (c1) and (c2), an oxide film 35
having a thickness of 0.1 μm is formed on the upper Si layer 31 in the
region A1. As the oxidation method, a wet oxide method (steam oxidation)
is used.

[0090]In FIG. 12, (a1) and (a2) illustrate the step d. (a2) is an R2-R2
cross-sectional view of (a1). The portion shown in (a1) in FIG. 12
corresponds to a region above the R3-R3 line of the mask M2 shown in FIG.
13. In the step d, patterning of the surface configuration of the AFM
tweezers 1 is performed using the mask M2 shown in FIG. 13. A comb shape
is formed in this step. After the patterning, etching is conducted to the
SiO2 layer 32 by ICP-RIE (Inductively coupled plasma-Reactive
Etching). By this etching, a narrow slit SL1 (in the direction of
<110> of the upper Si layer 31) in positions in which the tips of
the stationary arm 10 and the movable arm 20 is formed. The slit SL1 is
etched vertically with respect to the surface of the substrate.

[0091]In FIG. 12, (b1) to (b3) illustrate the step e. (b2) is an R4-R4
cross-sectional view. (b3) is an R5-R5 cross-sectional view. In the step
e, the exposed upper Si layer 31 is oxidized by the wet oxidation method.
Thereafter, in the step f shown in (a1) and (a2) in FIG. 14, the SiN film
34 is etched off by RIE with C2F6 to expose the upper Si layer
31 that remains as the underlying layer of the SiN film 34. (a2) in FIG.
14 is an R6-R6 cross-sectional view.

[0092]The oxide film 35 formed by the wet oxidation method serves as a
protective film for the upper Si layer 31 upon the etching of the SiN
film 34. Among the RIE conditions, the pressure of C2F6 gas is
increased to adjust etching selectivity between the SiN film 34 and the
oxide film 35, thereby removing only the SiN film 34 as shown in (a2) in
FIG. 14. As a result, the oxide film 35 that has been formed for
protection remains, so that only the upper Si layer 31 under the SiN film
34 is exposed.

[0093]In FIG. 14, (b1) and (b2) illustrate the step g. (b2) is an R7-R7
cross-sectional view. In the step g, the exposed upper Si layer 31 is
subjected to anisotropic etching with an aqueous 30% KOH solution. The
portion protected by the oxide film is not etched and only the upper Si
layer 31 is anisotropically etched to form a slant surface 310. As a
result, portions having a triangular cross-section corresponding to the
probe tip section 10B and the gripping section 20B are formed. As
mentioned above, the surface of the upper Si layer 31 is selected as the
main plane (001) of the single crystal Si, so that the slant surface 310
formed by the anisotropic etching is the {111} plane of single crystal
Si.

[0094]Etching is performed by ICP-RIE using the mask M3 shown in FIG. 15A
to remove unnecessary portions. Thereafter, the oxide film is etched off.
By the etching using the mask M3, the lengths of the probe tip section
10B and the gripping section 20B can be adjusted. Thereafter, unnecessary
portions on the lower Si layer 33 side are etched off by ICF-RIE from the
rear surface of the SOI wafer using the mask M4 shown in FIG. 15B. This
etching stops at the SiO2 layer 32. Then, unnecessary portions in
the SiO2 layer is removed with a hydrogen fluoride solution to
provide a configuration of the AFM tweezers 1 as shown in FIG. 16 (as
seen from the rear surface side).

[0095]In this stage, the observation probe 10B and the gripping probe 20B
have the same wedge shape. By processing the ridge portion of the
observation probe 10 by FIB (Focused Ion Beam), the wedge-shaped notch
100 as shown in FIGS. 3 and 8 is formed. FIG. 17 shows an example of the
method for processing the observation probe 10B using an FIB 400. The AFM
tweezers 1 are set in a predetermined direction so that the FIB 400 is
irradiated in a direction parallel to the notch surface 100a to be
formed. Then the FIB 400 is irradiated to an irradiation region 401 to
perform sputtering and when the depth of processing reaches a
predetermined value, the irradiation is stopped. In this manner, by using
FIB, there can be achieved notch processing in which the length and depth
of the notch as well as angle of the notch surface are controlled.

[0096]Instead of processing the notch 100 by FIB, the notch 100 may be
processed by a photolithographic process. On the surface of the Si layer
of the AFM tweezers 1 in the state as shown in FIG. 16 is formed an oxide
film 600 by the wet oxidation method. Then, the oxide film 600 in the
region where the notch 100 of the observation probe 10B is to be formed
is removed to expose the Si layer (a portion of the wedge-shaped probe).
The exposed Si layer is anisotropically etched with an aqueous 30% KOH
solution. As a result, the notch 100 as shown in FIG. 22B is formed in
the observation probe 102. Thereafter, the oxide film 60 is removed. FIG.
22C shows the observation probe 10B formed of the notch 100 in a side
view and a J-J cross-sectional view. The notch surface formed in the
notch section 100 by the anisotropic etching is the {111} plane of single
crystal Si.

[0097]Also, there may be used a method for forming the tweezers, in which
method after portions of the observation probe and of the driving probe
exclusive of the tips thereof are exposed, the exposed portions are
etched by dry etching, such as ICR-RIE, to a desired depth to form the
notch as shown in FIG. 23. In the case of ICP-RIE, the notch 100 is
etched vertically as shown in FIG. 23. By using ICP-RIE, notch processing
in which the length and depth of the notch are controlled can be
performed.

[0098]As mentioned above, the AFM tweezers 1 according to the present
embodiment is configured such that a sample is gripped by the gripping
surfaces of the observation probe 10B and the gripping probe 20B that are
parallel to each other. Accordingly, the gripping performance can be
improved. Since the notch 100 is formed in the portion of the lower ridge
of the observation probe 10B, occurrence of deformation of an AFM
observed image due to interference between the ridge and the sample can
be prevented. By designing the shape of the gripping probe 20B to be a
wedge shape (triangular prism) as shown in FIG. 9A, or the shape shown in
FIG. 9c, the observation performance can be improved while preventing the
gripping performance from being deteriorated.

Second Embodiment

[0099]By providing the notch 100 as mentioned above, there can be obtained
an image having less trailing without interference with the observation
probe 10B even when the height of the sample to be gripped is relatively
large. However, the tip of the observation probe 10B is wedge-shaped and
hence further sharpening of the probe tip is necessary in order to
perform image observation with high precision. On the other hand, further
sharpening of the probe tip leads to a decrease in size (d3) of the
gripping section 110, so that it is difficult to achieve stable gripping.

[0100]The notch surface of the notch 100 includes the notch surface 100b
that is parallel to the mounting surface of the observation stage and the
second notch surface 10a that passes through the tip of the ridge and is
vertical to the mounting surface. In the second embodiment, as shown in
FIG. 18A, a carbon nanotube (usually, a multiwall carbon nanotube) C1 is
attached as a probe tip to the second notch surface 100a. The carbon
nanotube C1 is attached vertically to a sample surface and the lower end
of the carbon nanotube C1 is made to protrude closer to the sample
surface side than the lowermost end of the observation probe 10B.

[0101]Upon gripping a sample, the observation probe 10B and the gripping
probe 20B (not shown) are set at predetermined heights (usually, lower
than a half of the height of the sample to be gripped). Usually, as shown
in FIG. 18B, the carbon nanotube C1 is elastically buckled to be bent. In
this state, the gripping of the sample by the tips of the probes is
performed. When the AFM tweezers 1 are drawn up after completion of the
gripping, the carbon nanotube C1 returns in the original shape without
damages. The carbon nanotube C1 can endure repeated buckling that is
repeated several hundreds times.

[0102]Although explanation has bee made on the example in which carbon
nanotube is used as the observation probe, similar effects can be
obtained with inorganic nanotubes such as one made of boron nitride (BN).

Third Embodiment

[0103]FIG. 19 illustrates a third embodiment of the present invention. To
improve observation performance, it is preferred that the probe tip T1 is
processed to be relatively thin by adjusting widths d4 and d3 to be small
so that the edges cross at a single point. However, when the probe tip T1
is made thinner, the gripping performance is decreased. Accordingly, in
the third embodiment, a second probe tip T2 is formed at a position
closer to the base of the probe than the first probe tip T1. A distance
d6 between the centers of the probe tips T1 and T2 is set smaller than
the length (the size in the direction along sample surface) of the sample
to be gripped. The probe tip T2 is formed such that the lower end of the
probe tip T2 is positioned by Δd higher than the lower end of the
probe tip T1. With this configuration, the probe tip T1 that protrudes
closer to the sample surface than the probe tip T2 serves as a probe tip
of AFM. In this case, Δd is set to a halt or less of the height of
averaged samples.

[0104]When a sample is gripped with the AFM tweezers 1 having the
above-mentioned configuration, the sample can be gripped at three
positions, i.e., an inner surface of the gripping probe 20B, an inner
surface of the probe tip T1 and an inner surface of the probe tip T2 of
the observation probe 10B. This is advantageous when gripping spherical
samples. In this case, the distance d6 is set to approximately the
diameter of the spherical sample. When the distance d6 between the two
probe tips T1 and T2 is set to a greater value, a longer sample can be
stably gripped. In this case, when the height of the sample is by
Δd higher than ever, occurrence of double tip image in which the
image of the tip is seen doubled is imperative. In this case, the
distance between the two images is equal to d6. Of the tip images in the
double tip image, one having better resolution is due to the sharpened
probe tip T1 and the other having worse resolution is due to the probe
tip T2. On the other hand, no double tip image is observed from a
substrate having the height of unevenness being smaller than Δd.
Therefore, position and height of the sample to be gripped and the
positional relationships between the two probe tips T1 and T2 are
determined from the double tip image.

[0105]The second probe tip T2 is formed as follows. First, a left side
notch 500a of the probe tip T2 shown in FIG. 19 is formed. Then, a notch
500b between the probe tips T1 and T2 is formed. Finally, the tip of the
second probe tip T2 is cut off such that the height (from the sample
surface) of the second probe tip T2 is by Δd greater than the
height of the first probe tip T1. Further, as necessary, the first probe
tip T1 is etched by FIB in order to set widths d4 and d3 relatively small
so that each edge of the observation probe 10B crosses at a single point,
thus sharpening the first probe tip T1.

[0106]While in the above description, explanation has been made on the
example in which the second probe tip T2 is formed by etching using FIB,
it would also be acceptable to fabricate it as follows. First, the notch
100 is etched by FIB to form the probe tip T1 on the tip of the
observation probe 10B. Further, the probe tip T1 is processed by FIB to
make the widths d4 and d3 relatively small and make the probe tip T1
thinner so that edges can cross at a single point. Then, an inclination
at which the AFM tweezers 1 are attached is adjusted such that the AFM
tweezers 1 are perpendicular to the sample surface and FIB is irradiated
at a distance d6 from the first probe tip T1 on the side of the base of
the probe at a decreased current density of FIB. On this occasion, a gas
such as an organometal gas or phenanthrene is introduced into the chamber
of the FIB device. The organometal gas or phenanthrene is decomposed to
deposit a metal or carbon along the irradiated ion beam to grow a
cylindrical structure. The diameter of the cylinder is about 100 nm. The
length of the cylinder can be controlled by setting time of irradiation
of the beam appropriately. The cylinder thus formed is used as the second
probe tip T2.

<<Adjustment of Matching Precision Between Observation Probe and
Gripping Probe>>

[0108]The matching precision of the observation probe 10B and the gripping
probe 20B can be improved by performing etching processing using FIB as
shown in FIG. 20. In FIG. 20, the AFM tweezers are mounted on a rotating
goniostage at an angle of 90° from their ordinary setting
position, and the observation probe 10B and the gripping probe 20b are
closed. In an image capturing mode of FIB, matching condition of the
lower ends of the tips of the two probes is observed from an appropriate
direction in which the tips are easily viewed. The matching state between
the observation probe 10B and the gripping probe 20B is observed and a
portion that does not match (shaded portion) is cut off in an etching
mode of FIB to adjust the matching state in the direction of lengths and
heights of the observation probe 10B and the gripping probe 20B.
Ordinarily, the notch is formed by FIB after the matching conditions of
the observation probe 10B and the gripping probe 20B are adjusted by the
above-mentioned operations.

[0109]In the above-mentioned embodiments, AFM tweezers 1 are fabricated by
processing a silicon substrate. However, the present invention is not
limited to such a method and the AFM tweezers 1 may be fabricated by
various fabrication methods. What is described above is only exemplary.
The present invention is not limited to the above-mentioned embodiments
and various modifications may be made to the present invention so far as
such modifications do not harm the features of the present invention.

[0110]According to the embodiments of the present invention, observation
with high resolution and high precision and stable gripping can be made
well balanced in a scanning probe microscope with AFM tweezers.